1. Field of the Invention
The present invention relates to color reproduction of an object of view in an electronic endoscope.
2. Description of the Related Art
Conventionally, there is an electronic endoscope which captures an object image by the color chip method, using a color CCD. An insert portion of the electronic endoscope is inserted into a body of a patient. A fiber bundle (light guide), which is a bundle of extra fine optical fibers, is penetrated through the insert portion. White illumination light, which is supplied from a light source device, is led to the tip of the insert portion by the light guide, and illuminates an object of view from the tip. The color CCD is provided with color chip filters having complementary colors (magenta, yellow, cyan, and green) which are arranged mosaically. Light reflected by the object is imaged on an image capturing plane of the color CCD through objective lenses. The imaged optical image is subjected to photoelectric conversion by the color CCD, whereby an image signal is output from the color CCD.
The electronic endoscope is connected to an image processing device. After the image signal is output from the color CCD, it is subjected to predetermined image processing in the image processing device. The image signal is then subjected to a multiplying operation in which it is multiplied by a predetermined matrix coefficient, and then the image signal is converted to an RGB signal which includes a red color component, green color component, and blue color component. A TV-monitor is connected to the image processing device. The RGB signal which is converted in the image processing device, is output to the TV-monitor. Consequently, a picture of the object is produced on a display of the TV-monitor.
Generally, a xenon lamp, a halogen lamp, a metal halide lamp, and so on, can be utilized as a light source of the above-mentioned white illumination light. These lamps have different spectral characteristics. Accordingly, when the picture is produced on the display of the TV-monitor after the processing by the image processing device, the color reproduction of the picture depends upon the light source. Therefore, the matrix coefficient which is used in the RGB conversion operation is adjusted in accordance with light source of the illumination light so that good color reproduction can be obtained.
Spectral sensitivity of complementary color filters of color CCDs overlaps at some frequencies. Accordingly, difference in the luminance brightness between some portions of the optical image of the object may cause discordance in the saturation of the complementary color filter. Due to this discordance, some colors of the object produced on the monitor may differ from their real color. Namely, even though the matrix coefficient is adjusted based on the kind of light source, luminance brightness conditions of the optical image may prevent the colors of some portions of the object from being precisely reproduced.